This invention relates generally to radiographic inspection and more particularly to a method of radiographic inspection of large objects such as airframes.
Aircraft, including their fuselages and nacelles, and other large structures, often require periodic inspection to verify their structural condition. This may be done visually or with non-destructive evaluation (NDE) techniques. Because of the complicated physical structure of aircraft fuselages and nacelles, radiographic inspection, such as X-ray inspection, is used to avoid the disassembly of overlapping components, insulation, wall coverings, etc. Modern digital electronic detectors are replacing X-ray film in many X-ray inspection applications. It is often difficult to position these detectors in contact with the inspected structure. Thus the detector and the structure are often not in physical contact and do not always move together. This results in blurred images and reduced ability to discern defects. This condition is further exacerbated with electronic detectors as geometric magnification and/or extended exposure times are sometimes used to improve image resolution. Both of these techniques increase sensitivity to any relative motion between the structure and the detector.
Unwanted motion is especially of concern in the inspection of very large objects such as airframes and aircraft engine nacelles. The physical size and arrangement of these objects results in the X-ray source and detector being mounted on different supports and thus having separate motion. Because of the large size of these objects, the X-ray source and detector mounting structures must be large enough to provide range of motion necessary to cover the entire object. For example, to inspect an aircraft fuselage, one might use a ground based cantilevered boom-like device to position the X-ray source or detector over the top of the fuselage. This would require a very large boom, over 30 feet in the case of a large aircraft. This extended reach device may have significant motion at the end of the boom, including vibration and harmonic motion from the residual inertia after movement of the device. Further, the large objects themselves often move during imaging. This may be due to wind, personnel working on the aircraft, and the like.
Accordingly, there is a need for a method to ensure the motion of the components during a radiographic imaging period is not large enough to negatively impact the quality of the image.